1. Field of the Invention
The invention relates to a hydraulic adjustable shock absorber with a work piston fastened to a piston rod, which divides the work cylinder into two work chambers filled with damping fluid, whereby there is a bypass valve parallel to the work cylinder.
2. Description of the Prior Art
Hydraulic telescoping vibration dampers are known, such as the types described in German Pat. No. 26 55 705 and German Pat. No. 27 44 301, in which a work chamber is divided into two partial chambers by a piston, whereby the damping piston exhibits the necessary mechanical valves for the production of damping force. Such a conventional vibration damper, however, has the disadvantage that the corresponding damping characteristic is fixed depending on the type of vehicle, and thereby must achieve a compromise between various vehicle conditions. Such a vibration damping of the vehicle with telescoping vibration dampers is correspondingly severely limited by the restricting parameters during operation, whereby different load conditions also have an effect on the system.
A process for active vibration damping is also known, as in German Laid Open Patent Application No. DE-OS 27 38 455, in which the damping force can be adjusted. A disadvantage here, however, is the fact that the damping losses must be replaced by means of an external pump. Such a system, with the addition of outside energy, requires an additional, externally-fed hydraulic system, and is therefore very expensive. Not all types of vehicles have, or will even accommodate, such an additional hydraulic system. Moreover, since the entire hydraulic system would fail if this external pump would fail, the vehicle may not be safe.
Electrically remote-controlled shock absorbers are also known, as described in German Patent Publication Published For Opposition Purposes No. DE-AS No. 14 05 781, in which the damping characteristic can be adjusted by means of a lifting magnet apparatus. Thus, the valve body modifies the cross section of a throttle. With such throttles in a bypass, throttle characteristics can be adjusted only gradually, so that as a result of the progressivity, parallel to the normal damping valves in damping pistons, a severely-restricted force-velocity curve variation of the vibration damper is achieved. In actual practice, it has been shown that such throttles are poorly suited to the satisfactory fulfillment of requirements for the variability of the damping force characteristics.